China's heir apparent Xi Jinping will meet US lawmakers critical ofBeijing on Wednesday before heading to the heartland state of Iowa for a reunion with ordinary Americans he met on a 1985 exchange.

US concerns over trade policy and human rights could come to the fore as Xi meets top US legislators in an election season that has seen Republican White House candidates accuse US President Barack Obama of being soft on Beijing.

Xi can expect a friendlier audience with business leaders later on Wednesday, when he gives a speech before traveling to Muscatine, Iowa to meet residents he came to know as a low-level official more than 25 years ago.

Obama, seeking reelection in November, on Tuesday met Xi, who is expected to assume the Chinese presidency in 2013, in a preview of a possible new era in the most crucial political and economic relationship of the 21st century.

The two men spoke for an extended Oval Office meeting of 85 minutes, as Xi was shepherded through a full program by US Vice President Joe Biden and enjoyed the rare honor of a 19-gun salute with booming cannons at the Pentagon.

The welcome, exceedingly rare for a mere vice president, reflected the importance Washington places on its relationship with Beijing, though did not paper over wide differences on economics and geopolitics.

And noisy protests from Tibetan protestors around the White House and the US Chamber of Commerce, where Xi gave a speech, reflected thorny human rights questions that have ruffled Sino-US relations for 40 years.

Obama said that Washington welcomed a "prosperous" China and praised its "extraordinary development over the last two decades," but stressed that rising power for Beijing came with "increased responsibilities."

He also stressed that the United States intended to remain a power in the Asia-Pacific region, following testy exchanges over China's territorial claims in the South China Sea during Obama's trip to Asia in November.

"We want to work with China to make sure that everybody is working by the same rules of the road when it comes to the world economic system," Obama said alongside a relaxed-looking Xi, as senior aides and translators stood by.

"That includes ensuring that there is a balanced trading flow not only between the United States and China but around the world," Obama said.

He also pledged Washington would "continue to emphasize what we believe is the importance of realizing the aspirations and rights of all people."

At a State Department luncheon Biden sharply criticized China's decision to join Russia in vetoing a UN resolution condemning violence in Syria, as well as Beijing's own rights record.

A senior Obama aide later said the president told Xi of his own disappointment with the Syria during the Oval Office talks.

Xi touched on the human rights question at the State Department, saying that China has made "tremendous and well-recognized achievements" in the area, but added: "There is always room for improvement."

"We will, in light of China's national conditions, continue to take concrete and effective policies and measures to promote social fairness, justice and harmony and push forward China's course of human rights," Xi said.

US observers will likely see those remarks as a restatement of China's conflicting definition of human rights and not as signaling a policy change.

The White House has spent months planning for the visit by Xi, who is expected to succeed Hu Jintao next year and could serve as president for a full decade in which China is expected to grow at breakneck speed.

But China is already in the firing line ahead of US elections in November, particularly on the economic issues.

US lawmakers accuse Beijing of keeping the value of its currency unfairly low to fuel inexpensive exports that have turned China into a manufacturing superpower.

At the luncheon, Xi said the United States and China "should address each other's economic and trade concerns through dialogue and consultation, not protectionism."

China has let its yuan appreciate since mid-2010 in response to concerns over inflation. But the United States wants China to do more and to take action in other areas including protection of US intellectual property.

In Iowa, Xi will attend a formal reception in the state capital Des Moines. The farming state counts on China as a rapidly growing market for its pork, soybeans and other produce.

In a briefing late Tuesday, Vice Foreign Minister Cui Tiankai said the two sides had agreed to meet on Asia-Pacific issues in March and had a "principled agreement" to hold a fourth strategic and economic dialogue in China in May.